The present invention relates to vacuum operated fluid pressure signal controllers and to controlling of exhaust gas recirculation (EGR) in an internal combustion engine by a vacuum actuated control valve.
In providing EGR for controlling emissions in automotive internal combustion engines, it is known to provide a valve for permitting exhaust gas to enter the engine induction manifold, which valve is controlled by a pressure responsive actuator receiving a fluid pressure control signal derived from an onboard source of subatmospheric pressure such as manifold vacuum.
It has been found that different amounts of EGR are required at the various engine speeds and loads encountered in automotive engine service. Where engine manifold vacuum has been the primary source of fluid pressure control signal for effecting EGR, it has been found that the high vacuum or low manifold absolute pressure (MAP) which occurs at idle or nearly closed throttle engine operation requires that the vacuum signal be cut off to the EGR Actuator in order to prevent an excess amount of EGR at low engine operating speeds.
Where engine manifold vacuum has been utilized as a primary control signal for EGR valve actuation, it has been found convenient to invert the sense of the change of vacuum with variations in engine speed and load by means of a vacuum inverter. An example of such a device which has been heretofore employed is that shown and described in the copending application Ser. No. 185,467, filed Sept. 9, 1980 in the names of Cyril Bradshaw and Martin Uitvlugt now U.S. Pat. No. 4,365,608 and assigned to the Assignee of the present invention. The aforementioned device provides, (once a threshold operating level of input signal is achieved), for a decreasing vacuum output signal in response to increasing manifold vacuum, or decreasing MAP.
However, even where a vacuum inverter is employed, the inverted manifold vacuum signal is sufficiently large in magnitude as to cause the actuator to provide opening of the EGR valve and thus excess EGR at idle or low operating engine speeds.
Furthermore, engine manifold vacuum can have identical values for two different engine operating speeds, for example, idle and moderate road speeds. Thus, if manifold vacuum is employed for a control signal, the same amount of EGR would be provided at two different engine speeds where different amounts of EGR are required.
In conjunction with utilizing engine manifold vacuum as a controller signal source, it has been desired to also utilize a secondary vacuum source for controlling EGR at idle or low engine operating speed. Such a source is found in present day gasoline spark ignited automotive engines in the so-called "ported" signal tap provided in the carburetor throat at the throttle plate. A ported vacuum signal is so named because it is vented or "ported" to the atmosphere above the throttle plate in the closed position and is exposed to carburetor throat vacuum in the throttle plate open position. Ported vacuum exhibits zero gauge or atmospheric pressure at engine idle and increases vacuum, or decreases MAP, rapidly with a relatively small amount of throttle opening until the ported signal equals engine manifold vacuum.
However, if a ported vacuum signal is employed for each EGR valve actuator control, the control signal is at the requisite null or atmospheric pressure for engine idle, but increases too rapidly with throttle opening to be useful for a control signal over a broad range of engine operating conditions.
Thus, it has long been desired to find a way of providing a fluid pressure control signal for an EGR valve actuator over a broad range of engine operating conditions beginning with idle and progressing through wide open throttle, at various engine speeds and provide the desired amount of EGR for the engine instantaneous engine operating condition. It has particularly been desired to find a way of utilizing the available ported vacuum signal in conjunction with an engine manifold vacuum, or MAP, to provide a suitable control signal over the entire regime of engine operating conditions.